Phosphor and vacuum ultraviolet excited luminescent element

ABSTRACT

A phosphor having high luminescence when excited by vacuum ultraviolet ray and a vacuum ultraviolet radiation excited light-emitting device comprising the phosphor. The phosphor comprises a metal oxide comprises at least one metal element M 1  selected from the group consisting of Ca, Sr and Ba, at least one metal element M 2  selected from the group consisting of Y, La, Gd and Lu, at least one metal element M 3  selected from the group consisting of Si and Ge and oxygen, and at least one metal element Ln 1  selected from the group consisting of Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Mn, as an activator.

TECHNICAL FIELD

The present invention relates to a phosphor and a vacuum ultravioletradiation excited light-emitting device comprising the phosphor. Moreparticularly, the present invention relates to the phosphor having highluminescence when excited by vacuum ultraviolet ray and to the vacuumultraviolet radiation excited light-emitting device comprising thephosphor.

BACKGROUND ART

Phosphors are used in a vacuum ultraviolet radiation excitedlight-emitting devices such as plasma display panels (hereafterabbreviated “PDP”) and rare gas lamps. Phosphors which emit lights underexcitation with vacuum ultraviolet rays have already been known. Forexample, BaMgAl₁₀O₁₇:Eu, Zn₂SiO₄:Mn and (Y,Gd)BO₃:Eu are practicallyused as a blue-emitting phosphor, a green-emitting phosphor and ared-emitting phosphor, respectively.

DISCLOSURE OF INVENTION

The object of the present invention is to provide a phosphor having highluminescence and suitable as the vacuum ultraviolet radiation excitedlight-emitting device.

Under this condition, as a result of research conducted by the presentinventors in an attempt to solve the above problems, it has been foundthat a phosphor has high luminescence when excited by vacuum ultravioletray. Thus the present invention has been completed.

That is, the present invention provides a phosphor comprising

-   a metal oxide comprises at least one metal element M¹ selected from    the group consisting of Ca, Sr and Ba, at least one metal element M²    selected from the group consisting of Y, La, Gd and Lu, at least one    metal element M³ selected from the group consisting of Si and Ge and    oxygen, and-   at least one metal element Ln¹ selected from the group consisting of    Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Mn, as an    activator.

Moreover, the present invention provides the vacuum ultravioletradiation excited light-emitting device comprising the above-mentionedphosphor

The phosphor of the present invention is excited by vacuum ultravioletray and shows high luminescence. Particularly, the phosphor ispreferably used in the vacuum ultraviolet radiation excitedlight-emitting device such as PDP and rare gas lamp. According to thepresent invention, the vacuum ultraviolet radiation excitedlight-emitting device having high luminescence is provided.

DETAILED DESCRIPTION OF THE INVENTION

The phosphor of the present invention comprises

-   a metal oxide comprises at least one metal element M¹ selected from    the group consisting of Ca, Sr and Ba, at least one metal element M²    selected from the group consisting of Y, La, Gd and Lu, at least one    metal element M³ selected from the group consisting of Si and Ge and    oxygen, and-   at least one metal element Ln¹ selected from the group consisting of    Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Mn, as an    activator,    wherein M¹ is a divalent metal, M² is a trivalent metal, and M³ is a    tetravalent metal.

The phosphor of the present invention comprises preferably a metal oxiderepresented by formula (I):M¹M² _(m)M³ _(n)O_((2+3m+4n)/2)  (I)wherein m is from 0.5 to 1.5 and n is from 0.5 to 2.5).

The phosphor of the present invention exhibits emission of differentcolors depending on the kind of metal element used as the activator andthe valence of the metal element. For example, when the activator is atrivalent Tb, the phosphor usually exhibits emission of green color. Inthis case, a part of the metal oxide M² is substituted with thetrivalent Tb.

When the activator is a divalent Eu, the phosphor usually exhibitsemission of blue color. In this case, a part of the metal oxide M¹ issubstituted with the divalent Eu. When the activator is a trivalent Eu,the phosphor usually exhibits emission of red color. In this case, apart of the metal oxide M² is substituted with the trivalent Eu.

The first group of preferable phosphors of the present inventioncomprises both a metal oxide represented by formula M¹ ₂M² ₂M³ ₂O₉ (m=1and n=1 in formula (I)) and activators of Ln¹ and Ln², and isrepresented by formula (II):(M¹ _(1-a)Ln² _(a))₂(M² _(1-b)Ln¹ _(b))₂M³ ₂O₉  (II)wherein Ln² is at least one element selected from the group consistingof Sm, Eu, Yb, and Mn, a is from 0 to 0.5, b is from 0 to 0.5, and thesum of a and b is not less than 0. Among the first group, a phosphor,which satisfies the condition of 0.03≦a+b≦0.3, is more preferable.

The second group of preferable phosphors of the present inventioncomprises both a metal oxide of the formula M¹ ₃M² ₂M³ ₂O₁₀ (m=⅔ and n=⅔in formula (I)) and activators of Ln¹ and Ln², and is represented byformula (III):(M¹ _(1-c)Ln² _(c))₃(M² _(1-d)Ln¹ _(d))₂M³ ₂O₁₀  (III)wherein Ln² is at least one element selected from the group consistingof Sm, Eu, Yb and Mn), c is from 0 to 0.5, d is a from 0 to 0.5 and thesum of c and d is not less than 0. Among the second group, a phosphor,which satisfies the condition of 0.03≦c+d≦0.3, is more preferable.

The third group of preferable phosphors of the present inventioncomprises both a metal oxide represented by formula M¹ ₃M² ₂M³ ₆O₁₈ (m=⅔and n=2 in formula (I)) and activators of Ln¹ and Ln², and isrepresented by formula (IV):(M¹ _(1-e)Ln² _(e))₃(M² _(1-f)Ln¹ _(f))₂M³ ₆O₁₈  (IV)wherein Ln² is at least one element selected from the group consistingof Sm, Eu, Yb, and Mn, e is from 0 to 0.5, f is from 0 to 0.5, and thesum of e and f is not less than 0. Among the third group, the phosphor,which satisfies the condition of 0.03≦e+f≦0.3, is more preferable.

The method for producing the phosphor of the present invention will beexplained below.

The method for producing the phosphor of the present invention is notspecifically limited, and the phosphor may be produced, for example, bycalcining a mixture of given metal compounds. The mixture of the givenmetal compounds is a mixture convertible to a phosphor comprising ametal oxide which comprises M¹, M², M³ and oxygen(O), and Ln¹. Thephosphor of the present invention is produced by weighing a M¹containing compound (such as calcium compound, strontium compound, orbarium compound), a M² containing compound (such as yttrium compound,lanthanide compound, gadolinium compound, or lutetium compound), a M³containing compound (such as silicon compound or germanium compound),and a Ln¹ containing compound (such as a compound which contains cerium,praseodymium, neodymium, promethium, samarium, europium, terbium,dysprosium, holmium, erbium, thulium, ytterbium or manganese) so as togive the desired composition, mixing these and calcining the mixture.

One of the preferable phosphors of the present invention, represented byformula Ca₂(Y_(0.95)Eu_(0.05))₂Si₂O₉, is produced, for example, byweighing calcium carbonate (CaCO₃), yttrium oxide (Y₂O₃), europium oxide(Eu₂O₃), and silicon oxide (SiO₂) so as to give that mole ratio ofCaCO₃:Y₂O₃:Eu₂O₃:SiO₂ is equal to 1:0.475:0.025:1 (mole ratio ofCa:Y:Eu:Si is 1:0.95:0.05:1) mixing these and calcining the mixtureunder air at about 1600° C.

The raw materials used for producing the phosphor of the presentinvention, that is, a calcium compound, a strontium compound, a bariumcompound, a yttrium compound, a lanthanum compound, a gadoliniumcompound, a lutetium compound, a silicon compound and a germaniumcompound, include hydroxides, carbonates, nitrates, halides andoxalates, of high purity (99% or higher by weight) which decompose athigh temperatures to be convertible to oxides, or oxides of high purity(99% or higher by weight).

Mixing of the raw material is usually conducted by using industriallyemployed ball mill, V-shape mixer, or stirring apparatus and the like.

When compounds such as hydroxides, carbonates, nitrates, halides,oxalate, which are convertible to oxides upon decomposition under air athigh temperature are used as the raw materials, they may be pre-calcinedbefore calcination. By pre-calcination a part of the above compounds inthe mixture may be decomposed or water in the mixture may be removed.Pre-calcination may be conducted at temperature of from about 600° C. toabout 900° C. The atmosphere used for the pre-calcination is notparticularly limited, and there may be used any of oxidizingatmospheres, reducing atmospheres and inert atmospheres such as nitrogenor argon.

The obtained mixture or further pre-calcined mixture is calcined.Calcination is usually conducted under conditions of the temperature offrom about 1000° C. to about 1700° C. for one hour to about 100 hours. Apreferable calcination atmosphere depends on the kind of activator. Forexample, when the activator is praseodymium, neodymium, promethium,dysprosium, holmium, erbium or thulium, the calcination atmosphere ispreferably an oxidizing atmosphere such as oxygen-containing argon, airand oxygen. When the activator is either cerium or terbium, thecalcination atmosphere is preferably a reducing atmosphere such asnitrogen which contains 0.1-10% by volume of hydrogen, or argon whichcontains 0.1-10% by volume of hydrogen. When the activator is amultivalent metal element such as europium, ytterbium, samarium, ormanganese, calcination is preferably conducted under the above-mentionedoxidizing atmosphere (such as oxygen-containing argon, air, oxygen) inviewpoint of heightening the valence of the metal element. On the otherhand, calcination is preferably conducted under the above-mentionedreducing atmosphere (such as nitrogen which contains 0.1-10% by volumeof hydrogen, argon which contains 0.1-10% by volume of hydrogen) inviewpoint of lowering the valence of metal element.

Calcination may be conducted in the presence of a proper amount of fluxto accelerate the reaction. Furthermore, calcination may be conductedtwice or more. Repetitive calcination may give phosphor particles withhigher crystallinity.

The calcined product is, if necessary, ground, deagglomerated, washed,or classified. Grinding and deagglomeration, for example, may beconducted by using a ball mill or a jet mill.

The phosphor of the present invention obtained by the above method, hashigh luminescence by excitation with vacuum ultraviolet rays, andtherefore, can be applied to a vacuum ultraviolet radiation excitedlight-emitting device such as a PDP and a rare gas lamp. The vacuumultraviolet radiation excited light-emitting device comprises phosphor,typically comprises the above-mentioned phosphor, a plate and anelectrode. More practically, the vacuum ultraviolet radiation excitedlight-emitting device comprises a rear plate, an address electrode, abarrier rib, a protective layer, a dielectric layer, a transparentelectrode, a bus electrode, and a glass front plate.

A PDP comprising the phosphor of the present invention may be producedby a known method disclosed in Japanese Patent Application Laid-open No.10-195428. Each of blue-emitting, green-emitting and red-emittingphosphors for vacuum ultraviolet radiation excited light-emittingdevices is mixed with a binder comprising a cellulose compound, apolymer such as polyvinyl alcohol, and an organic solvent to prepare aphosphor paste. Each of the resulting paste is coated on an innersurface of a rear plate provided with address electrodes which is formedin a stripe shape by barrier ribs and on the surface of the barrier ribsby screen printing or the like followed by calcining at from 300° C. to600° C. to form the respective phosphor layers. Thereon is superposed asurface glass plate provided with a dielectric layer and a protectivelayer on the inner surface thereof so that transparent electrodes andbus electrodes thereof are arranged in the direction perpendicular tothe phosphor layers, and the superposed surface glass plate is bonded tothe rear plate. The inside evacuated and a rare gas of low pressure suchas Xe or Ne is sealed therein to form discharge spaces. Thus, a PDP isobtained.

EXAMPLE

The present invention will be explained in more detail by followingexamples, which should not be constructed as limiting the invention inany manner.

REFERENCE EXAMPLE

Calcium carbonate (CaCO₃, manufactured by Wako Pure Chemical IndustriesLtd.), europium oxide (Eu₂O₃, manufactured by Shin-Etsu Chemical Co.,Ltd.), magnesium carbonate (MgCO₃, manufactured by Kyowa ChemicalIndustries Ltd.), and silicon oxide (SiO₂, manufactured by Wako PureChemical Industries Ltd.) were weighed so as to give a mole ratio ofCaCO₃:MgCO₃:Eu₂O₃:SiO₂=0.97:1:0.015:2 and these were mixed.

The mixture was calcined under argon(Ar) containing 2% by volume ofhydrogen (H₂) at 1400° C. for 2 hours to obtain a phosphor representedby formula (Ca_(0.97)Eu_(0.03))MgSi₂O₆.

The obtained phosphor was placed in a vacuum chamber, the inside ofwhich was kept at a vacuum of 6.7 Pa (5×10⁻² Torr) or lower, wasirradiated with ultraviolet rays using an excimer 146 nm lamp (ModelH0012, manufactured by Ushio Inc.). The phosphor emits blue color andthe luminance thereof was assumed to be 100.

Example 1

Calcium carbonate (CaCO₃, manufactured by Wako Pure Chemical IndustriesLtd.), yttrium oxide (Y₂O₃, manufactured by Shin-Etsu Chemical Co.,Ltd.), europium oxide (Eu₂O₃, manufactured by Shin-Etsu Chemical Co.,Ltd.), and silicon oxide (SiO₂, manufactured by Wako Pure ChemicalIndustries Ltd.) were weighed so as to give a mole ratio ofCaCO₃:Y₂O₃:Eu₂O₃:SiO₂=0.95:0.5:0.025:1 and these were mixed. The mixturewas calcined under argon (Ar) containing 2% by volume of hydrogen (H₂)at 1400° C. for 2 hours to obtain a phosphor represented by formula(Ca_(0.95)Eu_(0.05))₂Y₂Si₂O₉ (M¹ is Ca, M² is Y, M³ is Si, Ln² is Eu, ais 0.05 and b is 0 in formula (II)).

The obtained phosphor was placed in a vacuum chamber, the inside ofwhich was kept at a vacuum of 6.7 Pa (5×10⁻² Torr) or lower, wasirradiated with ultraviolet rays using an excimer 146 nm lamp (ModelH0012, manufactured by Ushio Inc.). The phosphor emits blue color andthe luminance thereof was 108.

Example 2

Calcium carbonate (CaCO₃, manufactured by Wako Pure Chemical IndustriesLtd.), yttrium oxide (Y₂O₃, manufactured by Shin-Etsu Chemical Co.,Ltd.), europium oxide (Eu₂O₃, manufactured by Shin-Etsu Chemical Co.,Ltd.), and silicon oxide (SiO₂, manufactured by Wako Pure ChemicalIndustries Ltd.) were weighed so as to give a mole ratio ofCaCO₃:Y₂O₃:Eu₂O₃:SiO₂=1:0.475:0.025:1 and these were mixed. The mixturewas calcined under air at 1600° for 2 hours to obtain a phosphorrepresented by formula Ca₂(Y_(0.95)Eu_(0.05))₂Si₂O₉ (M¹ is Ca, M² is Y,M³ is Si, Ln¹ is Eu, a is 0 and b is 0.05 in formula (II)).

The obtained phosphor was placed in a vacuum chamber, the inside ofwhich was kept at a vacuum of 6.7 Pa (5×10⁻² Torr) or lower, wasirradiated with ultraviolet rays using an excimer 146 nm lamp (ModelH0012, manufactured by Ushio Inc.). The phosphor emits red color and theluminance thereof was 125.

Example 3

Calcium carbonate (CaCO₃, manufactured by Wako Pure Chemical IndustriesLtd.), yttrium oxide (Y₂O₃, manufactured by Shin-Etsu Chemical Co.,Ltd.), cerium oxide (CeO₂, manufactured by Shin-Etsu Chemical Co.,Ltd.), and silicon oxide (SiO₂, manufactured by Wako Pure ChemicalIndustries Ltd.) were weighed so as to give a mole ratio ofCaCO₃:Y₂O₃:CeO₂:SiO₂=1:0.475:0.05:1 and these were mixed. The mixturewas calcined under air at 1400° C. for 2 hours to obtain a phosphorrepresented by formula Ca₂(Y_(0.95)Ce_(0.05))₂Si₂O₉ (M¹ is Ca, M² is Y,M³ is Si, Ln¹ is Ce, a is 0 and b is 0.05 in formula (II)).

The obtained phosphor was placed in a vacuum chamber, the inside ofwhich was kept at a vacuum of 6.7 Pa (5×10⁻² Torr) or lower, wasirradiated with ultraviolet rays using an excimer 146 nm lamp (ModelH0012, manufactured by Ushio Inc.). The phosphor emits blue color andthe luminance thereof was 107.

1. A phosphor represented by formula(M¹ _(1-a)Ln² _(a))₂(M² _(1-b)Ln¹ _(b))₂M³ ₂O₉ wherein M¹ is at leastone metal element selected from the group consisting of Ca, Sr, and Ba,M² is at least one metal element selected from the group consisting ofY, La, Gd, and Lu, M³ is at least one metal element selected from thegroup consisting of Si and Ge and oxygen, Ln¹ is at least one metalelement selected from the group consisting of Ce, Pr, Nd, Pm, Sm, Eu,Tb, Dy, Ho, Er, Tm, Yb, and Mn, Ln²is at least one element selected fromthe group consisting of Sm, Eu, Yb, and Mn, a is from 0 to 0.5, b isfrom 0 to 0.5, and the sum of a and b is not less than
 0. 2. A phosphorrepresented by formula(M¹ _(1-c)Ln² _(c))₃(M² _(1-d)Ln¹ _(d))₂M³ ₂O₁₀ wherein M¹ is at leastone metal element selected from the group consisting of Ca, Sr, and Ba,M² is at least one metal element selected from the group consisting ofY, La, Gd, and Lu, M³ is at least one metal element selected from thegroup consisting of Si and Ge and oxygen, Ln¹ is at least one metalelement selected from the group consisting of Ce, Pr, Nd, Pm, Sm, Eu,Tb, Dy, Ho, Er, Tm, Yb, and Mn, Ln² is at least one element selectedfrom the group consisting of Sm, Eu, Yb and Mn, c is from 0 to 0.5, d isa from 0 to 0.5, and the sum of c and d is not less than
 0. 3. A vacuumultraviolet radiation excited light-emitting device comprising thephosphor according to claim 1 or 2.